Classic lesion studies in rats identified two hypothalamic regions as a "dual centre" for feeding. What were their proposed functions?
A: Lateral hypothalamus (LH) = satiety centre (lesions → overeating); ventromedial hypothalamus (VMH) = hunger centre (lesions → starvation)
B: Lateral hypothalamus (LH) = hunger centre (lesions → aphagia/starvation); ventromedial hypothalamus (VMH) = satiety centre (lesions → hyperphagia/obesity)
C: Both LH and VMH are hunger centres; the satiety signal comes entirely from peripheral hormones, not the brain
D: Anterior hypothalamus = hunger; posterior hypothalamus = satiety, with no involvement of the LH or VMH
Correct: Lateral hypothalamus (LH) = hunger centre (lesions → aphagia/starvation); ventromedial hypothalamus (VMH) = satiety centre (lesions → hyperphagia/obesity)
The classic "dual centre" model proposed two hypothalamic regions with opposing functions: the lateral hypothalamus (LH) as the "feeding centre" — LH lesions produced aphagic (non-eating) rats that starved without force-feeding, and LH stimulation triggered eating — and the ventromedial hypothalamus (VMH) as the "satiety centre" — VMH lesions produced hyperphagic rats that became markedly obese. Though this simple model has been substantially revised (the effects of LH lesions are partly due to disrupting fibre tracts, and feeding is now understood as a distributed circuit), it established the hypothalamus as the central locus of energy regulation. Modern research has identified specific neuronal populations — ARC nucleus NPY/AgRP neurons (hunger-promoting) and POMC neurons (satiety-promoting) — as more precise targets.
Ghrelin and leptin are peripheral hormones that signal hunger and satiety to the brain. Which statement correctly describes them?
A: Ghrelin is secreted by fat cells (adipocytes) and rises with increasing fat stores; leptin is secreted by the stomach and rises before meals
B: Ghrelin is secreted by the stomach, rises before meals, and signals hunger; leptin is secreted by adipocytes and signals fat stores — high leptin suppresses appetite
C: Both ghrelin and leptin are secreted by the hypothalamus; ghrelin acts on peripheral organs to increase appetite, leptin acts on gut to slow digestion
D: Ghrelin and leptin both promote appetite; satiety signals come exclusively from gut peptides (GLP-1, CCK)
Correct: Ghrelin is secreted by the stomach, rises before meals, and signals hunger; leptin is secreted by adipocytes and signals fat stores — high leptin suppresses appetite
Ghrelin is secreted primarily by the stomach and rises sharply before anticipated meals, acting on hypothalamic ARC neurons (activating NPY/AgRP neurons) to stimulate appetite and promote fat storage. It is the only known peripheral hormone that stimulates hunger — sometimes called the "hunger hormone." Leptin is secreted by white adipose tissue in proportion to fat stores; it acts on hypothalamic POMC neurons to suppress appetite and increase energy expenditure. Leptin was initially celebrated as a potential anti-obesity drug, but most obese individuals are leptin-resistant (high circulating leptin, but the brain fails to respond). Rare congenital leptin deficiency (as in ob/ob mice and some human cases) causes severe early-onset obesity, dramatically reversed by leptin administration.
What does set point theory propose about body weight regulation, and what is a key criticism of it?
A: Set point theory proposes that weight is entirely determined by caloric intake; the criticism is that genetics also plays a role
B: Set point theory proposes each individual has a biologically defended weight; the body compensates for deviations through metabolism and appetite adjustments. Criticism: modern food environments can override the set point upward ("settling point" theory)
C: Set point theory predicts that weight is impossible to change permanently because the brain always returns to the set point; criticism is that bariatric surgery proves this wrong
D: Set point theory has no empirical support and has been completely replaced by the CICO (calories in/calories out) model
Correct: Set point theory proposes each individual has a biologically defended weight; the body compensates for deviations through metabolism and appetite adjustments. Criticism: modern food environments can override the set point upward ("settling point" theory)
Set point theory proposes that body weight is biologically regulated around a target value, with compensatory mechanisms — changes in metabolic rate, appetite, and energy expenditure — that resist deviations in either direction. Evidence includes: metabolic adaptation to caloric restriction (reduced BMR after weight loss), increased ghrelin and reduced leptin after weight loss (opposing maintenance of lower weight), and the regain of weight in most people following dieting. The primary criticism is that set points are not truly fixed: modern food environments — characterised by highly palatable, energy-dense, heavily marketed food — appear to ratchet set points upward over time ("settling point" model). Bariatric surgery is also notable because it appears to lower the set point, not merely restrict intake, producing durable weight loss without constant compensatory hunger.
The mesolimbic dopamine system is central to motivation and reward. What distinguishes "wanting" from "liking" in Kent Berridge's incentive salience theory?
A: "Wanting" (dopamine) and "liking" (opioids) are identical: both are activated by the same stimuli and produce the same behaviour
B: "Wanting" (incentive salience, driven by mesolimbic dopamine) is the motivational drive to pursue reward; "liking" (hedonic pleasure, driven by opioid and endocannabinoid systems) is the pleasurable experience of reward — they can dissociate
C: "Wanting" is a conscious process mediated by the prefrontal cortex; "liking" is an unconscious signal from the nucleus accumbens
D: "Wanting" refers to habitual reward-seeking; "liking" refers to novel reward-seeking. Both depend on dopamine.
Correct: "Wanting" (incentive salience, driven by mesolimbic dopamine) is the motivational drive to pursue reward; "liking" (hedonic pleasure, driven by opioid and endocannabinoid systems) is the pleasurable experience of reward — they can dissociate
Kent Berridge's incentive salience theory distinguishes two components of reward: "wanting" — the motivational drive to seek a reward, mediated by mesolimbic dopamine (VTA → nucleus accumbens, striatum) — and "liking" — the hedonic pleasure experienced when consuming the reward, mediated by endogenous opioid and endocannabinoid systems in the nucleus accumbens. Crucially, wanting and liking can dissociate: dopamine-depleted rats still show hedonic "liking" responses (positive facial expressions) to sweet taste but lose the motivation to work for food. Conversely, dopamine activation (as with amphetamine) potently increases wanting/craving without necessarily increasing liking/pleasure. This dissociation helps explain addiction: repeated drug use may escalate dopaminergic wanting while hedonic tolerance reduces liking — a cycle of compulsive craving without satisfaction.
Homeostatic drive theory (Hull, 1943) proposes that biological needs create internal states that motivate behaviour. What is its core claim and limitation?
A: All motivation is homeostatic; drive theory explains both primary (hunger, thirst) and secondary (achievement, curiosity) motivations equally well
B: Physiological needs create internal "drives" that motivate corrective behaviour to restore homeostasis; the limitation is that it cannot account for incentive motivation (seeking reward even when no deprivation exists) or curiosity/exploration
C: Drive theory predicts that all motivation comes from external incentives, not internal needs; its limitation is underestimating internal hunger signals
D: Drive theory correctly predicts all motivated behaviour in humans; modern neuroscience has confirmed its core claims without modification
Correct: Physiological needs create internal "drives" that motivate corrective behaviour to restore homeostasis; the limitation is that it cannot account for incentive motivation (seeking reward even when no deprivation exists) or curiosity/exploration
Clark Hull's drive reduction theory proposed that biological needs (hunger, thirst, pain, cold) create internal drive states (physiological arousal/tension) that motivate behaviour aimed at reducing the drive (eating, drinking, escape). Drive reduction is reinforcing — behaviours that reduce drives are strengthened. The theory accounts well for basic biological motivations and fits operant conditioning. However, it cannot explain: (1) incentive motivation — organisms will work for rewards even without deprivation (you eat dessert even when not hungry); (2) curiosity and exploration — animals explore novel environments without any drive to reduce; (3) sensation-seeking — humans often increase arousal rather than reduce it. Incentive motivation theory (Bindra; Toates) and the Berridge wanting/liking framework better account for the full range of motivated behaviour.
Which hormone primarily drives sexual motivation in both males and females, and where is it produced?
A: Oestrogen in females (from ovaries) and progesterone in males (from testes)
B: Testosterone (an androgen), produced primarily in the testes in males and in ovaries and adrenal glands in females
C: Oxytocin, produced in the hypothalamus and released from the posterior pituitary, drives sexual arousal in both sexes
D: Prolactin from the anterior pituitary, which peaks during sexual arousal and drives approach behaviour
Correct: Testosterone (an androgen), produced primarily in the testes in males and in ovaries and adrenal glands in females
Testosterone — the primary androgen — is the key hormonal driver of sexual motivation in both males and females, despite being present at much lower concentrations in females. In males, testosterone is produced mainly by Leydig cells in the testes (and to a lesser extent by adrenal glands); in females, by the ovaries (theca cells) and adrenal glands. In females, testosterone (and its conversion to oestrogen via aromatase) drives sexual desire. Women who undergo oophorectomy (ovary removal) experience reduced sexual desire restored by androgen supplementation. In males, testosterone levels correlate with libido; hypogonadism reduces sexual motivation, restored by testosterone replacement. The medial preoptic area (MPOA) of the hypothalamus is a critical integration centre for testosterone's effects on sexual motivation and behaviour in both sexes.
What is the sexually dimorphic nucleus (SDN) and what does research on it suggest about biological sex differences in the brain?
A: A region of the cortex responsible for gender identity, consistently larger in males and invariably absent in females
B: A cluster of neurons in the medial preoptic area of the hypothalamus that is typically larger in males than females in many mammalian species, and is influenced by prenatal sex hormone exposure
C: A region of the amygdala that controls fear responses and is larger in males, explaining higher rates of aggression
D: A nucleus in the brainstem that controls sexual behaviour exclusively; it has no structural sex differences but shows functional differences in activity levels
Correct: A cluster of neurons in the medial preoptic area of the hypothalamus that is typically larger in males than females in many mammalian species, and is influenced by prenatal sex hormone exposure
The sexually dimorphic nucleus of the preoptic area (SDN-POA) was first described by Roger Gorski and colleagues in 1978 in rats: it is 5–8 times larger in males than females and develops under the influence of testosterone during a perinatal critical period. The "organisational" effect of prenatal testosterone shapes neural structure permanently; subsequent "activational" effects of adult testosterone then influence behaviour. In humans, INAH3 (interstitial nucleus of the anterior hypothalamus 3) — putative human equivalent — was found by Simon LeVay (1991) to be smaller in gay men than in heterosexual men, suggesting a possible biological basis for sexual orientation. The SDN is involved in male-typical sexual behaviour (specifically the medial preoptic area, MPOA, integrates testosterone signals and controls copulatory behaviour). Research in this area remains contested, particularly in humans, due to small sample sizes and complexity of defining sexual orientation.
The nucleus accumbens (NAcc) is described as the brain's "reward hub." What makes it a convergence point for multiple motivational systems?
A: It is the only brain structure that receives serotonergic projections, making it uniquely sensitive to mood fluctuations
B: It receives convergent input from the VTA (dopamine), prefrontal cortex (cognitive context), hippocampus (memory), amygdala (emotional significance), and hypothalamus (homeostatic state), integrating these to produce motivated action
C: It is where all conscious emotional experiences are generated; it does not receive projections but rather generates output to all motivational circuits
D: It functions exclusively as a motor output structure, translating motivational signals from the striatum into movement toward rewards
Correct: It receives convergent input from the VTA (dopamine), prefrontal cortex (cognitive context), hippocampus (memory), amygdala (emotional significance), and hypothalamus (homeostatic state), integrating these to produce motivated action
The nucleus accumbens (ventral striatum) acts as an interface between motivation and action. It receives dopaminergic input from the VTA (ventral tegmental area) — the core "reward" signal; glutamatergic input from the prefrontal cortex (contextual information, planning); from the hippocampus (memory of past reward outcomes); from the basolateral amygdala (emotional salience); and from the hypothalamus (homeostatic state: hunger, thirst, sexual arousal). These convergent inputs allow the NAcc to integrate "what I want," "what I remember about this," "what context I'm in," and "how deprived I am" to generate an appropriate motivational state and drive behaviour via output to motor circuits. All major drugs of abuse converge on the mesolimbic system, producing dramatic dopamine release in the NAcc — hijacking the natural reward circuit.
Hunger, Motivation & Sexual Behaviour
Classic lesion studies in rats identified two hypothalamic regions as a "dual centre" for feeding. What were their proposed functions?
About this quiz
From the gnawing pull of hunger to sexual motivation and the dopaminergic pull of reward, biological drives shape behaviour in fundamental ways. The hypothalamus is the master regulator — integrating hormonal signals, energy balance, and reproductive state to direct goal-directed behaviour.
This quiz covers the biology of hunger and satiety (hypothalamic circuits, leptin and ghrelin, set point theory), the reward system and motivation (dopamine, nucleus accumbens, wanting vs liking), and the biological basis of sexual behaviour.